If the blockchain is rescanned for a single block (i.e. start and stop hashes are equal, and with that also the estimated start/stop verification progress values) the progress calculation could lead to a NaN value caused by a division by zero (0.0/0.0), resulting in an invalid JSON result for the getwalletinfo RPC. This PR fixes this behaviour by setting the progress to zero in that special case. Fixes #20297.
The behaviour can easily be reproduced by continuously running single block rescans in an endless loop, e.g. via
#!/bin/bash
while true
do
bitcoin-cli rescanblockchain $(bitcoin-cli getblockcount)
done
and at the same time perform some getwalletinfo RPCs.
On the master branch, this leads to frequent invalid responses (tested on mainchain):
$ bitcoin-cli getwalletinfo
error: couldn't parse reply from server
$ curl --user `cat ~/.bitcoin/.cookie` --data-binary '{"jsonrpc": "1.0", "id": "curltest", "method": "getwalletinfo", "params": []}' -H 'content-type: text/plain;' http://127.0.0.1:8332/
{"result":{"walletname":"","walletversion":169900,"format":"bdb","balance":0.00000000,"unconfirmed_balance":0.00000000,"immature_balance":0.00000000,"txcount":0,"keypoololdest":1603677276,"keypoolsize":1000,"hdseedid":"3196e33ecb47c7130e6ca60f2f895f9259860dca","keypoolsize_hd_internal":1000,"paytxfee":0.00000000,"private_keys_enabled":true,"avoid_reuse":false,"scanning":{"duration":0,"progress":},"descriptors":false},"error":null,"id":"curltest"}
(note that missing value for "progress" in the JSON result).
On the PR branch, the behaviour doesn't occur anymore.
